Definition
An onboard alerting system that monitors an aircraft's height above terrain using radio altimeter data and other inputs, and provides the flight crew with aural and visual warnings when the aircraft is in a flight configuration that risks an unintended collision with the ground.
Plain English
A safety system in the aircraft that watches how close you are getting to the ground and shouts a warning if it thinks you are about to fly into it.
Context Anchor
Pilots encounter this term in aircraft equipment descriptions, cockpit warning discussions, and accident-prevention training involving flight near terrain.
Derivation
Proximity comes from a Latin word meaning “nearest” or “very close.” In this term, it points to the system’s job: warning the crew when the aircraft is too near the ground for the situation.
Why Pilots Care
It prevents controlled flight into terrain, a leading cause of fatal accidents, by giving the crew time to react before impact.
Analogy
It is like a backup warning sensor in a car, but for an aircraft near the ground. The important difference is that in an airplane, the warning may require an immediate climb or correction.
Intuition Check
Do not read “ground proximity” as only meaning closeness during landing. The system warns whenever being near the ground or terrain becomes unsafe for the aircraft’s flight path.
Example Sentence 1
Shortly after takeoff, the captain reduced the rate of descent in response to a Ground Proximity Warning System alert.
Example Sentence 2
During the night instrument approach the crew monitored the ground proximity warning system for any sudden drop in terrain clearance.